Patterns of spatial distribution of Callinectes sapidus in invaded environments of the Valencian coast (Spain)

• ¹ Polytechnic University of Valencia, Spain
• ² University of Alicante, Spain

Introduction Callinectes sapidus (Rathbun, 1896) is a portunid crab native of estuarine systems in the Western Atlantic coast, capable of reaching sizes up to 20 cm in carapace width. This species typically lives segregated by size to avoid cannibalism and it has a complex life cycle in which males remain in estuarine systems and females move to saltier waters to spawn and hatch. Planktonic larvae live in open waters and return to estuaries to settle as juvenile crabs. It is a euryhaline predator with high diet plasticity, which gives its high invasive potential. Its presence in the Mediterranean has been documented since the 1950s, but in recent decades, the population started to expand rapidly. In the Mediterranean coast of Spain, the first crab was captured in 2012 in the Ebro’s Delta. In the Albufera of Valencia, a coastal lagoon that is communicated with the sea by three channels equipped with floodgates, the first crab was captured in 2014, and since then catches have increased annually. This is of special concern because the Albufera of Valencia is a protected environment under Spanish regulation, and the presence of the blue crab might endanger the local fisher’s livelihood, both by inflicting damage to the fishing gear and through competition with target species like Anguilla anguilla. There is another established blue crab population. In Gandia, a coastal locality 70 km south of the Albufera. Therefore, our aims were i) to determine the population structure and spatial segregation by sex in these two different areas and ii) to study if this species behaviour is different from the one it shows on its native distribution area. Methods In both locations, Albufera and Gandia, fishery independent (baited traps) and fishery dependent data (commercial catches) have been collected since 2017. Fishermen in the Albufera of Valencia use traps known as “mornell”, whereas in Gandia blue crabs are caught in trammel nets located in the coastal area close to the harbour. Our baited traps were deployed in different locations inside the Albufera of Valencia and also in the channels that connect the lagoon to the sea. In Gandia, traps were deployed in the San Nicolás ravine that connects the inner part of the harbour with the sea. In both locations the salinity was recorded and used in the sampling design implemented in the Albufera of Valencia. Results Spatial segregation by sex and size were clear in both areas, with males showing a strong association to the lower salinity areas while females preferred saltier waters. In the lower salinity areas, between 80% and 90% of the catch were males, whereas in the higher salinity areas up to 90% of the catches were females. However, salinity ranges were very different between locations, varying from 0‰ to 2‰ inside the Albufera lagoon and up to 24‰ in the channels that connect the lagoon to the sea whereas in Gandia, salinity ranged from 20‰ - 30‰ in the part of the port connecting to the ravine to 37.5‰ in the coastal area. Spatial segregation by sex happened both at salinities between 0‰ and 24‰ in the Albufera, and between 20‰ and 37.5‰ in Gandia. Discussion In its native distribution area C. sapidus lives in big estuaries with gradual salinity changes, but in the Mediterranean coast there are only strongly stratified estuaries, areas with sudden salinity changes (floodgates) or small salinity variations due to the contribution of small rivers, ravines or groundwaters. In the estuaries of the Atlantic coast of America, females do not move away from the mouth of estuaries and return in these after the reproductive events. However, off Gandia, females remain in the marine environment after the reproductive period and spend a period of inactivity buried in shallow sandy sediments. Salt waters are essential to ensure egg viability and larval survival, but it is not necessary to have large estuaries to complete the life cycle of the species. The segregation by size is a strategy to avoid cannibalism and besides the need of females for saltier waters, these factors could explain the apparent change in the life cycle of the species. It would be very interesting to deepen the knowledge of the migration patterns and the spatial segregations linked to the need for habitat use (underwater vegetation in juveniles, etc.) to complete the life cycle in an invaded environment which is so different from the original environment.